As expected, U.S. President Donald Trump signed a bill on Wednesday that imposed fresh sanctions on Russia, North Korea and Iran even as he expressed concern that the "seriously flawed" legislation "will drive China, Russia, and North Korea much closer together."

South Korean stocks led the way lower. They have shown repeated ability this year to shrug off North Korean provocations, including its string of missile launches. Coming into Thursday, the Kospi was one of the region's best-performing indexes, rising 20% and topping highs set in 2011.

But it slid 1.8% in morning trading amid a 3.3% drop in index giant Samsung Electronics, more than erasing the week's gains. The drop came as the Samsung conglomerate's de facto head testified for the first time at his corruption trial.

For the market at large in Korea, the prospect of higher corporate and personal income taxes is also weighing on sentiment, said Andrew Bresler, deputy head of sales trading for Asia-Pacific at Saxo Capital. The Kospi logged its worst day of the year on Friday in falling 1.7%.

The fresh drop Thursday fueled morning declines in the country's well-performing currency; the dollar was recently up 0.5% versus the won.

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Taiwan stocks also saw profit-taking on Thursday, after being a standout on Wednesday following Apple's strong quarterly report. The Taiex declined 0.5% after hitting 27-year highs a day earlier.

Declines were more modest elsewhere. Indexes in Australia, China and Hong Kong were all off 0.2% in morning trading. Japan's Nikkei, meanwhile, eased 0.4% to move back to 20000 amid some fresh gains in the yen; the dollar eased back to Yen110.60.

Analysts also said stock buying would be somewhat muted Thursday ahead of the Bank of England's policy meeting later in the day.